Channel Access Indication Method and Device to Avoid Unnecessary Probe Delay

1. A channel access indication method, comprising: receiving, by a first communications device, a channel synchronization request sent by a second communications device, wherein the channel synchronization request requests the first communications device to send a synchronization frame to the second communications device, and a wake-up receiver is configured for the second communications device; and according to the channel synchronization request and a time at which the second communications device is woken up and that is learned by the first communications device based on preset signaling, sending, by the first communications device when a channel is idle, the synchronization frame to the woken-up second communications device, wherein the synchronization frame instructs the woken-up second communications device to access the channel after receiving the synchronization frame, wherein there are a plurality of woken-up second communications devices, and the synchronization frame is sent in response to the channel synchronization request based on the time at which the second communications device is woken up, and the synchronization frame carries predetermined information including an identifier of the one or more woken-up second communications device, wherein the sending, when a channel is idle, of the synchronization frame to the woken-up second communications device comprises: sending, by the first communications device when the channel is idle, a first synchronization frame to one or more of the plurality of woken-up second communications devices; and sending, by the first communications device when the channel is idle, a second synchronization frame to the plurality of woken-up second communications devices, wherein the first synchronization frame includes the identifier of the one or more woken-up second communications device, and the second synchronization frame does not include the identifier, wherein a receiver address of the second synchronization frame is a broadcast address.

2. The method according to claim 1 , wherein the first synchronization frame instructs the one or more woken-up second communications device to wait a first preset duration to access the channel after receiving the first synchronization frame, and the first preset duration is a short inter-frame space (SIFS).

3. The method according to claim 1 , wherein the second synchronization frame instructs each woken-up second communications device to wait a second preset duration to perform a backoff procedure to contend for access to the channel after receiving the second synchronization frame, and the second preset duration is a distributed coordination function inter-frame space (DIFS).

4. The method according to claim 1 , wherein the sending, when a channel is idle, of the synchronization frame to the woken-up second communications device further comprises: sending, by the first communications device when the channel is idle, a third synchronization frame to the plurality of woken-up second communications devices, wherein the third synchronization frame carries a sub-channel resource indication of each woken-up second communications device and the identifier of each woken-up second communications device; a receiver address of the third synchronization frame is a broadcast address; and the third synchronization frame instructs the plurality of woken-up second communications devices to wait a first preset duration to simultaneously access the channel based on their respective sub-channel resource indications after receiving the third synchronization frame.

5. The method according to claim 1 , wherein the sending, when a channel is idle, of the synchronization frame to the woken-up second communications device further comprises: sending, by the first communications device when the channel is idle, a physical layer legacy preamble L-Preamble to the plurality of woken-up second communications devices, wherein the L-Preamble carries first indication information and all or a portion bits of a check code field of a wake-up frame that is received by wake-up receivers of the plurality of woken-up second communications devices to wake up main transceivers of the plurality of second communications devices; the first indication information indicates, to the plurality of woken-up second communications devices, that the L-Preamble is a synchronization frame; the all or the portion bits of the check code field indicate the identifiers of the plurality of woken-up second communications devices; and the L-Preamble instructs the plurality of woken-up second communications devices to wait a second preset duration to perform a backoff procedure to contend for access to the channel after receiving the L-Preamble.

6. The method according to claim 1 , wherein the synchronization frame further includes a physical layer legacy preamble L-Preamble, wherein the L-Preamble carries first indication information and all or a portion bits of a check code field of a wake-up frame received by a wake-up receiver of the woken-up second communications device; the first indication information indicates, to the second communications device, that the L-Preamble is a synchronization frame; and the all or the portion bits of the check code field indicate the identifier of the woken-up second communications device.

7. The method according to claim 1 , the synchronization frame further includes any one of a clear-to-send CTS frame, a request-to-send RTS frame, or a trigger frame; and the synchronization frame carries the identifier of the woken-up second communications device.

8. The method according to claim 1 , wherein the first synchronization frame is any one of a clear-to-send (CTS) frame, a request-to-send (RTS) frame, or a trigger frame.

9. The method according to claim 1 , wherein the receiving, by a first communications device, of the channel synchronization request sent by a second communications device comprises: receiving, by the first communications device, an association request frame sent by the second communications device, wherein the association request frame carries indication information of the channel synchronization request of the second communications device.

10. The method according to claim 1 , wherein the receiving, by a first communications device, of the channel synchronization request sent by a second communications device comprises: receiving, by the first communications device, a management frame or a control frame sent by the second communications device or a control frame sent by the second communications device, wherein the management frame or the control frame carries indication information of the channel synchronization request.

11. A channel access indication device comprising: a first communications device, the first communications device comprising: a receiver configured to receive a channel synchronization request sent by a second communications device, the channel synchronization request requests the first communications device to send a synchronization frame to the second communications device, and a wake-up receiver is configured for the second communications device; and a processor configured to: according to the channel synchronization request and a time at which the second communications device is woken up and that is learned by the first communications device based on preset signaling, instruct a transmitter to send, when a channel is idle, the synchronization frame to the woken-up second communications device, and the synchronization frame instructs the woken-up second communications device to access the channel after receiving the synchronization frame, wherein there are a plurality of woken-up second communications devices, and the synchronization frame is sent in response to the channel synchronization request based on the time at which the second communications device is woken up, and the synchronization frame carries predetermined information including an identifier of the one or more woken-up second communications device, wherein when the channel is idle, the transmitter is configured to send: a first synchronization frame to one or more of the plurality of woken-up second communications devices; and a second synchronization frame to the plurality of woken-up second communications devices, wherein the first synchronization frame includes the identifier of the one or more woken-up second communications device, and the second synchronization frame does not include the identifier, wherein a receiver address of the second synchronization frame is a broadcast address.

12. The device according to claim 11 , wherein the receiver is configured to receive a management frame or a control frame sent by the second communications device, and the management frame or the control frame carries indication information of the channel synchronization request.

13. The device according to claim 11 , the first synchronization frame instructs the one or more woken-up second communications devices to wait a first preset duration to access the channel after receiving the first synchronization frame, and the first preset duration is a SIFS.

14. The device according to claim 11 , wherein the second synchronization frame instructs each woken-up second communications device to wait a second preset duration to perform a backoff procedure to contend for access to the channel after receiving the second synchronization frame, and the second preset duration is a DIFS.

15. The device according to claim 11 , wherein the transmitter is further configured to send, when the channel is idle, a third synchronization frame to the plurality of woken-up second communications devices, wherein the third synchronization frame carries a sub-channel resource indication of each woken-up second communications device and the identifier of each woken-up second communications device; a receiver address of the third synchronization frame is a broadcast address; and the third synchronization frame instructs the plurality of woken-up second communications devices to wait a first preset duration to simultaneously access the channel based on their respective sub-channel resource indications after receiving the third synchronization frame.

16. The device according to claim 11 , wherein the transmitter is further configured to send, when the channel is idle, a physical layer legacy preamble L-Preamble to the plurality of woken-up second communications devices, wherein the L-Preamble carries first indication information and all or a portion bits of a check code field of a wake-up frame that is received by wake-up receivers of the plurality of woken-up second communications devices to wake up main transceivers of the plurality of second communications devices; the first indication information indicates, to the plurality of woken-up second communications devices, that the L-Preamble is a synchronization frame; the all or the portion bits of the check code field indicate the identifiers of the plurality of woken-up second communications devices; and the L-Preamble instructs the plurality of woken-up second communications devices to wait second preset duration to perform a backoff procedure to contend for access to the channel after receiving the L-Preamble.

17. The device according to claim 11 , wherein the synchronization frame further includes a physical layer legacy preamble L-Preamble, wherein the L-Preamble carries first indication information and all or a portion bits of a check code field of a wake-up frame received by a wake-up receiver of the woken-up second communications device; the first indication information indicates, to the second communications device, that the L-Preamble is a synchronization frame; and the all or the portion bits of the check code field indicate the identifier of the woken-up second communications device.

18. The device according to claim 11 , wherein the synchronization frame further includes any one of a clear-to-send (CTS) frame, a request-to-send (RTS) frame, or a trigger frame, and the synchronization frame carries the identifier of the woken-up second communications device.

19. The device according to claim 11 , wherein the first synchronization frame is any one of a clear-to-send (CTS) frame, a request-to-send (RTS) frame, or a trigger frame.

20. The device according to claim 11 , wherein the receiver is configured to receive an association request frame sent by the second communications device, and the association request frame carries indication information of the channel synchronization request of the second communications device.